The North Union Railway resulted from the first railway amalgamation in British history. The two companies were the Wigan Branch Railway and the Wigan and Preston Junction Railway.

The line was fully opened in 1838 and ran from Parkside, near Warrington, northwards to Preston via Wigan. The North Union Railway eventually came into the joint ownership of the London and North Western Railway (LNWR) and the Lancashire and Yorkshire Railway (LYR).

The North Union Viaduct has a significant influence on Miller Park. The bridge was designed by Charles Vignoles, built in 1836-8 and was opened in 1838. The form was influenced by Waterloo Bridge, London (which has now been replaced), and was regarded throughout the nineteenth century as one of the finest and most substantial bridges in England. The viaduct was 873 feet long, 28 feet wide and 68 feet above the bed of the river. It contained 675,000 cubic feet of rusticated aslar brought from quarries in Whittle, Longridge and Lancaster and cost £40,000.

The bridge was not completed when the first passengers on the Preston-Wigan line passed over it in 1838. The North Union trains soon proved that they could go as fast as 30 m.p.h. The traveling time to Wigan was cut from over three hours to under half an hour.

In all the line cost £500,000, or £21,000 per mile. The bridge is now part of the West-Coast Main Line.

A close up of the North Union Viaduct over the Ribble, taken in 1863. Through the arches can be seen the viaduct carrying the East Lancashire Railway across the flood plain south of the river. It was subsequently transformed into the embankment that can be seen today.

In this photograph, taken in 1862 the bridge of the East Lancashire Railway can be seen through the arch, with the large houses of Avenham at the top of the slope beyond. It has been altered and widened on two occasions, but its scale and proportions are still impressive.